The present invention relates, in general, to substrates used for interior trim and especially to headliner substrates for motor vehicles, and in particular, to a new and useful headliner substrate and process for making the same, where the entire article of manufacture is made of synthetic fibers such as, but not limited to polyester (PET), polypropylene (PP), and nylon that enables it to be 100% recyclable or can be made 100% recyclable.
U.S. Pat. No. 5,022,943 and 5,134,014, and U.S. patent application Ser. No. 08/755,283 filed Nov. 22, 1996, which are all incorporated here by reference, disclose methods, structures and materials for composite substrates of the type to which the present application relates.
Substrates for interior trim are known to be manufactured from various natural and synthetic fibers. In particular, headliners are known which are made from corrugated fiberboard and thermoplastic composites. The composite may include an upper kraft paper layer and intermediate thermoplastic film layer (e.g. polyester or polyethylene), an inner kraft liner, an inner thermoplastic layer, and a corrugated fiberboard medium.
It is also known to use fiberglass in a headliner for its strength, dimensional stability and acoustic absorption characteristics. Further, it is also known to use polyurethane foam sandwiched between two glass mats for its strength and dimensional stability of the glass mats and for acoustical enhancement of the foam. It is also known to use polyester mat sandwiched between glass mats again for its strength and dimensional stability as well as for its acoustical enhancement. Finally, attempts have been made to use only polyester mats, however, dimensional stability and structural rigidity could not be maintained without incurring exorbitant costs or without using glass mats to increase the rigidity and dimensional stability of the overall product. In today's market, there is no one product that can currently meet the stringent demands of the automotive industry, which are a low cost, lightweight interior trim substrate with superior acoustical performance and moldability while passing the dimensional stability and transverse strength requirements while also being 100% recyclable.
The main reason to develop an all synthetic fiber headliner is because it can meet all the aforementioned requirements while still providing the ability for the entire headliner to be 100% recyclable. Current attempts to develop an all synthetic fiber interior trim substrate has been supplied using a thick mat of high melt polyester fibers mixed with low melt PET fibers called binder fibers. This mat is then thermoformed in a hot molding die, then transferred to a marriage tool where a polyester non-woven cosmetic cover material is bounded to the polyester fiber substrate. Please see U.S. patent application Ser. No. 08/755,283 for details concerning these dies and tools.
In some processes, the mat is preheated with hot air blowing or radiating heat through the substrate. During the heating process, the low melt PET binder fibers soften whereby binding together the high melt PET fibers. The temperature is not high enough to soften the high melt fibers. The composite is then placed into a molding die in conjunction with the polyester cosmetic covering material and formed and bonded simultaneously. This system yields a 100% polyester headliner which is 100% recyclable. Also, due to the fibrous nature and high loft of the substrate, it performs very well as sound absorber and has excellent molding.
Currently in the automotive industry, fibrous material such as fiberglass is considered the benchmark for sound absorption. However, due to the potential undesirable characteristics of the glass fibers during the processing of the substrate as well as in the final product, the automotive industry is attempting to eliminate fiberglass type products as an interior trim substrate. Resinated cotton or shoddy and phenolic impregnated polyester fibers both have proven to be effective sound absorption substrates; however, both products use phenolic resin as a strengthening and binder agent which are considered to be undesirable due to the formaldehyde and odor this product produces as well as its non-recyclable characteristic. Synthetic fibers are seen as a major alternative to eliminate the undesirable effect of fiberglass and phenolic impregnated fibers.
Cost is the major prohibitive issue in today's all polyester interior trim substrate. Polyester fibers are very expensive compared to other substrates available on the market. Furthermore, in order to attain a substrate thickness of 15-20 mm (as required for superior sound absorption), a very thick mat must be used prior to compression, otherwise, there will not be enough pressure to bond enough binder fibers together, resulting in a headliner that will not have the integrity to pass the automotive specifications for transverse strength as well as through the environmental chambers. As a result, in order to enable the current product to pass the specification, the percentage of binder fibers which as double the cost of the matrix fibers must be increased and simultaneously the amount of mass must be increased. Although this product became a salable product that is 100% recyclable, the product is neither cost effective nor light weight. This leads to the primary reason for the present invention.